# COMPUTATIONAL MOLECULAR SPECTROSCOPY OF FeCN IN THE $^6\Delta$ ELECTRONIC GROUND STATE

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 Title: COMPUTATIONAL MOLECULAR SPECTROSCOPY OF FeCN IN THE $^6\Delta$ ELECTRONIC GROUND STATE Creators: Hirano, Tsuneo; Okuda, Rei; Nagashima, Umpei; Amano, Michiko; Mitsui, Yukari; Itono, Sachiko S.; Jensen, Per Issue Date: 2007 Publisher: Ohio State University Abstract: We have previously reported a computational molecular spectroscopic study of $^6\Delta_i$ FeNC,}pirko, and P. Jensen, \textit{J. Mol. Spectrosc.}, \textbf{236}, 234-247 (2006).} where we showed that the experimentally derived, too-short C-N bond length ($r_{\rm e}$(C-N) = 1.03(8) {\AA})}, \textbf{114}, 2137-2143 (2001).} can be ascribed to an inadequate treatment of the large amplitude bending motion in the experimental determination of $r_0$. Here, we report analogous calculations for $^6\Delta_i$ FeCN.}, \textit{in press} (2007).} Based on the three-dimensional potential energy surface calculated at the MR-SDCI+Q+$E_{\rm rel}$/[Roos ANO (Fe), aug-cc-pVQZ (C, N)] level of theory, the standard spectroscopic parameters of Fe$^{12}$CN and Fe$^{13}$CN are derived by perturbation methods, and ro-vibrationally averaged bond lengths $\langle r \rangle$ have been predicted as expectation values obtained with ro-vibrational wavefunctions from the MORBID program. Some of the spectroscopic constants thus determined are: $r_{\rm e}$(Fe-C) = 2.048 {{\AA}} and $r_{\rm e}$(C-N) = 1.168 {\AA}, $\omega_{1}=2179$ cm$^{-1}$, $\omega_{2}=173$ cm$^{-1}$, $\omega_{3}=420$ cm$^{-1}$, dipole moment = 4.59 D, spin-orbit coupling constant $A_{\rm SO}=-83$ cm$^{-1}$, $\langle r\mbox{(Fe-C)}\rangle_{0}$ = 2.082 {\AA}, and $\langle r\mbox{(C-N)}\rangle_{0}$ = 1.172 {\AA}. In variational MORBID calculations, rovibronic energy levels are determined, and some vibrational bands are simulated. The bending potential is shallow, and the MORBID calculations show that the zero-point averaged structure is bent with the expectation value $\langle \angle\mbox{(Fe-C-N)} \rangle_{0}$ $=$ 170(5)$^irc$ (where the number in parentheses is the quantum-mechanical uncertainty). We compare the $^6\Delta_i$ FeCN results with those obtained for $^6\Delta_i$ FeNC. Since there are no experimental spectroscopic data available for FeCN, we hope that the predictions made here may be useful in the experimental investigation of this molecule. Description: Author Institution: Research Institute for Computational Sciences, National; Institute of Advanced Industrial Science and Technology,; 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan; Department of Chemistry, Faculty of Science, Ochanomizu University,; 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan; Theoretische Chemie, Bergische Universitat,; D-42097 Wuppertal, Germany URI: http://hdl.handle.net/1811/31311 Other Identifiers: 2007-WH-07